Project 4 proposes a systematic evaluation of 335 children with spina with spina meningomyelocele and hydrocephalus (SBH) who partial agenesis or hypoplasia (thinning) of the corpus callosum. Partial agenesis occurs in about 65% of children with SBH as part of the defect in neuroembryogenesis, while hypoplasia occurs in 30% as a consequence of hydrocephalus. Consequently, Project4 proposes the largest evaluation of children significant with corpus callosum anomalies ever attempted. To accomplish this objective, children will be classified into groups defending of whether they are missing the rostrum (n=70), splenium (n=48), or both rostrum and splenium (n=100), or have only hypoplasia (n=100). In addition, a small group of children (n=17) with SBH who have a normal corpus callosum and 96 normal controls will be studied. Each child will receive measure of interhemispheric transfer in three modalities: 1) visual (tachotoscopic presentation of CVC trigrams and nonverbal forms); 2) auditory (dichotic listening for words); 3) tactile localization, naming and matching). In addition, interhemispheric transfer time and interhemispheric transfer of visuomotor information will be measured. For each of these five studies, specific hypotheses concerning callosal subgroup differences are made. The interhemispheric transfer tasks are also related to the area measure of the corpus callosum and the size of the anterior commissure, the latter representing a potential compensatory mechanism for reorganization of function. Children with congenital deficits of the corpus callosum show reorganization of function but these functions are not normal. Project4 promises to elucidate important information on callosal functioning and brain reorganization after congenital insult with specific application to children and adults with SBH.